MSE-536

Protein Interactions with Biomaterials

Topics:

•Thermodynamics of Protein Adsorption

•Protein Structure

•Protein Transport and Adsorption Kinetics

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ThermodynamicsFor a reaction to spontaneously occur, the change

in Gibbs free energy, G, must be <0:

Surfsolprotads GGGG

STHG

G = Gibbs free energy

H = enthalpy (energy available to do work)

S = entropy (disorder)

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Thermodynamics of Protein Adsorption

Hydrophobicity: Hydrophobic areas attract hydrophobic areas

Charge: Opposite charges attract

Size: Larger molecules have more active sites

Structure: the stability (strength of intramolecular bonds) and molecule unfolding rate

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Surface features and their interactions with proteins:

• Topography: greater texture means greater interaction

• Composition: Chemistry governs types of interactions

• Hydrophobicity: hydrophobic surfaces bind more protein

• Heterogeneity: non-uniform surfaces have many different types of domains to interact with proteins

• Potential: surface charge affects charge distributions of ions in solution and proteins

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Protein StructureProteins are

polymeric chains of amino acids.

Amino acids have a central carbon atom attached to a hydrogen, a carboxyl group

(COOH) and an amine group (NH2)

Each of the 20 standard amino acids have a one-

letter symbol. A sequence of three symbols, as shown for RNA (right) is called a

codon

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The pK value is related to the pH of the amino acid. Higher values are more

acidic (lower pH)

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Proteins (polypeptides) are

formed from condensation

reactions between amino acids

(peptide bonds).

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Secondary Structures

-helix

pleated structure

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Tertiary and Quaternary StructuresInteractions between side chains control how the protein folds in three and four dimensions. These interactions include:

•Covalent bonding

•Ionic interactions

•Hydrogen bonding

•Hydrophobic interactions

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Protein Transport and Adsorption Kinetics

Four main types of protein transport:

1. Diffusion

2. Thermal convection

3. Flow (convective transport)

4. Coupled transport (combinations of 1-3)

A concentration gradient drives diffusion, while a

temperature gradient creates thermal convection

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2

21

2

R

r

R

QV

The velocity profile is given by:

Diffusion is Fick’s 2nd law, with the addition of a contribution from flow:

r

Cr

rrD

dz

dCV

dt

dC 1

Here in cylindrical coordinates

V = velocity = viscosity

Q = volumetric flow rate

C = concentration

D = diffusivity

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Initial absorption rate is high on a clean surface

Rate slows as surface becomes covered

Further absorption occurs as molecules rearrange to create

new free surface

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Protein exchange on a material surface.

The initial protein (light gray) is wedged out of the way by the newer proteins (dark gray), which have a greater

affinity for the material